An inflatable device of the above kind is known from GB-A-2251929 in the form of a plastics bag that is inflated via a tube that opens into the bag via a seal in the wall of the bag. An elastic strip which is secured within the bag with one of its ends in the mouth of the inflation tube and the other end attached to the wall of the bag opposite the tube-mouth, stretches during inflation to provide positive pressure within the bag for maintaining the bag pressing against the inside surface of the chimney flue or other duct.
Manufacture of the inflatable device of GB-A-2251929 requires the secure attachment of the elastic strip in the mouth of the tube and to the inside wall of the bag opposite. This, together with the sealing of the tube through the wall of the bag, has been found difficult to accomplish reliably and economically in assembly of the device. It is one of the objects of the present invention to provide a form of inflatable device for blocking a chimney flue or other duct, by which this difficulty can be overcome